Apparatus for hazardous waste vitrification

ABSTRACT

Apparatus (10) and a method for vitrifying hazardous waste includes a melting vessel (12) in which hazardous waste and any other necessary components for forming a glassy mixture upon heating are introduced for heating by a heater (38), and a metallic containment vessel (46) of the apparatus receives the melting vessel so as to receive and contain any material that exits the melting vessel upon failure. A voltage is applied across spaced electrical connections (72) of the melting vessel (46) to heat material within the melting vessel. Any failure of the melting vessel (12) is detected by a sensor (48). A stirrer (39) can be utilized to mix the material (18) during the heating. The containment vessel (46) is preferably hermetically sealed around the melting vessel (12) to contain gases as well as any melted material received from the failed melting vessel (12). The sensing of the failure can be either by a pressure change in the hermetically sealed chamber (58) or by sensing of the presence of material received by the containment vessel (46) from the failed melting vessel (12) such as by electrical circuit type detection.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of application Ser. No.246,412 entitled "Apparatus and Method for Vitrification of HazardousWaste", filed on May 20, 1994 by Kenneth H. Wetmore, Kenneth R.Kormanyos and Stephen F. Cox, now U.S. Pat. No. 5,536,114.

TECHNICAL FIELD

This invention relates to apparatus and a method for vitrifyinghazardous waste.

BACKGROUND ART

Vitrification of waste materials has previously been accomplished inceramic lined melting vessels that are capable of being heated torelatively high temperatures such as on the order of about 1500° C. to1600° C. Such heating as disclosed by U.S. Pat. No. 4,820,328 Roberts etal can be utilized to vitrify waste asbestos by a high temperaturemelting process. Furthermore, as disclosed by U.S. Pat. No. 5,100,453Richards such high temperature melting can be utilized to recycle glassfibers such as of the type utilized for building insulation. Likewise,incinerator fly ash can also be vitrified by such high temperaturemelting in a ceramic melting vessel. During such processing, the wasteand any other necessary components to form a glassy material uponheating are introduced into the ceramic melting vessel, and the meltedmaterial permeates into seams or any cracks in the ceramic meltingvessel sufficiently to cool and thereby seal the vessel so that there isno leakage.

Vitrification of hazardous waste at a lower temperature such as on theorder of about 1000° to 1100° C. has also previously been done byheating thereof within a metallic melting vessel. When hazardous wastesuch as nuclear waste or heavy metals etc. is vitrified, the resultantmelted mixture can be delivered into a container for storage uponcooling. However, the metallic melting vessel can fail during use and,in such case, hazardous waste in the melting vessel can contaminate thefacility in which the processing is being performed. Such contaminationcan be a particular problem when nuclear waste processing is involved.Furthermore, heating in a metallic melting vessel has previously beendone by passing an electrical current through the melted materialbetween the metallic melting vessel and a stirrer that mixes thematerial being heated. Thus, the metallic melting vessel and the stirreract as the electrodes between which the current flows for the heating asmixing takes place.

DISCLOSURE OF INVENTION

Objects of the present invention are to provide improved apparatus and amethod for vitrifying hazardous waste in a manner that providescontainment of the waste in case of failure of the melting vessel inwhich the hazardous waste is heated for the vitrification.

In carrying out the above objects, apparatus for vitrifying hazardouswaste in accordance with the present invention includes a metallicmelting vessel for receiving hazardous waste and any other necessarycomponents for forming a glassy material upon heating. A heater of theapparatus includes spaced electrical connections for providing a voltageacross the metallic melting vessel to provide heating of material in themelting vessel. The apparatus also includes a metallic containmentvessel in which the melting vessel is located so the containment vesselupon failure of the melting vessel receives and contains any materialthat exits the melting vessel due to its failure. A sensor of theapparatus is located externally of the melting vessel and at leastpartially externally of the containment vessel to detect failure of themelting vessel. The preferred embodiment has the metallic melting vesselmade of an alloy of platinum and rhodium when the melting temperatureinvolved is above about 1100° C., and having the melting vessel made ofan alloy of nickel and chromium when the melting temperature involved isbelow about 1100° C.

The apparatus for vitrifying hazardous waste is also disclosed asincluding a stirrer for mixing the material being heated.

In the preferred construction of the apparatus, the containment vesselis hermetically sealed around the melting vessel to form an enclosedchamber that contains gases as well as any other material that exits thefailed melting vessel.

Different embodiments of the sensor are disclosed. In one embodiment,the sensor is communicated with the hermetically sealed chamber betweenthe melting vessel and the containment vessel to detect a change inpressure within the hermetically sealed chamber when the melting vesselfails to thereby detect such failure. In other embodiments, the sensorfor detecting failure of the melting vessel senses the presence ofmaterial received by the containment vessel from the failed meltingvessel and preferably includes an electrical circuit that detects thepresence of material received by the containment vessel from the failedmelting vessel. In one embodiment, the electrical circuit of the sensorincludes a pair of electrical probes that are located between themelting and containment vessels and are normally electrically isolatedfrom each other until material received by the containment vessel fromthe failed melting vessel electrically connects the probes to eachother. In another embodiment, the electrical circuit includes a flowpath that is located between the melting and containment vessels andthat is normally closed but is opened by the presence of materialreceived by the containment vessel from the failed melting vessel.

In the preferred construction, the apparatus also includes anothersensor for sensing failure of the melting vessel so as to provide afail-safe detection of the melting vessel failure. Thus, there is a pairof sensors for detecting the failure of the melting vessel, and eachsensor is preferably either a sensor that is communicated with thehermetically sealed chamber between the melting vessel and thecontainment vessel to sense a change in pressure when the melting vesselfails, or a sensor including an electrical circuit that senses thepresence of material received within the containment vessel from thefailed melting vessel.

In carrying out the objects of the invention, the method for vitrifyinghazardous waste is performed by introducing hazardous waste and anyother necessary components for forming a glassy material upon heatinginto a metallic melting vessel. A voltage is applied across the metallicmelting vessel to heat within the melting vessel. The melting vessel isalso located within a metallic containment vessel so as to contain anymaterial that exits the melting vessel due to failure of the meltingvessel. Sensing for a failure of the melting vessel is also performed toprovide an indication that the processing should be terminated so thatthe hazardous waste does not contaminate the facility in which theprocessing is being performed.

In performing the method for vitrifying hazardous waste, the materialcan also be stirred during the heating.

In one preferred practice of the method, the sensing for failure of themelting vessel is performed by detecting a change in pressure of thehermetically sealed chamber between the melting and the containmentvessels.

In another preferred practice of the method, the sensing for failure ofthe melting vessel is performed by detecting the presence of materialreceived within the containment vessel from the failed melting vessel.The presence of material received within the containment vessel from thefailed melting vessel is disclosed as being detected by an electricalcircuit.

The most preferred practice of the method utilizes a pair of sensors todetect failure of the melting vessel so that this detection is performedin a fail-safe manner.

The objects, features and advantages of the present invention arereadily apparent from the following detailed description of the bestmodes for carrying out the invention when taken in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an elevational view taken in section through apparatusconstructed in accordance with the present invention to provide themethod thereof for vitrifying hazardous waste;

FIG. 2 is a view that illustrates a pressure sensor for detectingfailure of a melting vessel of the apparatus;

FIG. 3 is a view that illustrates a normally open electrical circuitsensor for sensing the failure of the melting vessel; and

FIG. 4 is a view that illustrates a normally closed electrical circuitsensor for sensing the failure of the melting vessel.

BEST MODES FOR CARRYING OUT THE INVENTION

With reference to FIG. 1, apparatus 10 constructed in accordance withthe present invention performs the method thereof for vitrifyinghazardous waste such as nuclear waste, heavy metals etc. This apparatusincludes a metallic melting vessel 12 having an inlet 14 for receivinghazardous waste and any other necessary components for forming a glassymaterial upon heating as is hereinafter more fully described. Themelting vessel 12 also has a gas outlet 16 through which gases generatedby the processing can flow outwardly for any necessary treatment priorto being released to the atmosphere. Molten material 18 within thevessel 12 is delivered through an outlet 20 with a lower entry end 22and an upper outer exit end 24 with a construction that functions like ateapot spout. Outlet 20 which has a tubular construction outwardly ofthe melting vessel 12 extends through a suitable heating insulation 26secured by an outer shell 28, and the outlet 20 is also surrounded by aheater 30 to maintain the material molten until it is delivered to asuitable container for cooling and consequent solidification. Likewise,a lower drain 32 of a metallic tubular construction extends through theinsulation 26 and is surrounded by an associated heater 34 with itsouter end closed by a water cooled plug 36 that can be removed to permitdrainage of the melting vessel 12 when necessary.

Heating of the material within the melting vessel 12 of apparatus 10 isaccomplished by a heater 38. More specifically, the metallic meltingvessel 12 includes electrical connections 72 spaced from each other andacross which an electrical voltage is applied to heat material withinthe melting vessel. The melting vessel 12 thus acts as an electricresistance element in providing the heating. The melting vessel 12 ispreferably made of an alloy of platinum and rhodium to provide thecapability of high temperature heating above about 1100° C. This hightemperature allows the use of higher temperature melting glasses some ofwhich have a longer lifetime against breakdown and/or a higher wasteloading capability and thus are advantageous in vitrification ofradioactive hazardous waste such as plutonium containing components. Themelting vessel 12 is preferably made of an alloy of nickel and chromiumwhen using glass compositions having melting temperatures below about1100° C. Specific nickel and chromium alloys that can be used are soldby Inco Alloys International, Inc. of Huntington, W. Va., United Statesof America, under the trademark INCONEL. One such alloy is designatedINCONEL 601 and has a composition in parts by weight of: aluminum--1part, chromium--23 parts, iron--14 parts, and nickel--61 parts. Anothersuch alloy is designated INCONEL 690 and has a composition in parts U.S.Ser. No. 08/675,338by eight of: chromium 29 parts, iron--9 parts, andnickel--62 parts.

A metallic containment vessel 46 of the apparatus 10 shown in FIG. 1 islocated around the melting vessel 12 so the containment vessel uponfailure of the melting vessel receives and contains any material thatexits the failed melting vessel. Thus, any hazardous waste component ofmaterial that exits the failed melting vessel 12 will not contaminatethe facility in which the apparatus 10 is located but, rather will becontained within the containment vessel 46 which can then be properlyprocessed during a clean-up operation. Furthermore, apparatus 10 alsoincludes at least one sensor 48 for detecting failure of the meltingvessel as is hereinafter more fully described.

With continuing reference to FIG. 1, it will be noted that both themetallic melting vessel 12 and metallic containment vessel 46 arerespectively made from metal plates 50 and 51 that are secured by welds52 with these two vessels essentially being unitized with each otherafter completion of the assembly. Lower supports 54 provide thenecessary support between the floor plates 50 and 51 while a support rod55 extends downwardly from the containment vessel floor plate 51 throughthe insulation 26 to provide support for the unitized melting andcontainment vessels 12 and 46. Suitable unshown supports between thesidewall plates 50 and 51 of the melting and containment vessels 12 and46 are also provided and like all of the plates and supports are securedby associated welds.

As illustrated in FIG. 1, the apparatus 10 can also be provided with astirrer 39 for mixing the material 18 being heated such as by rotationas shown by arrow 39'.

With continuing reference to FIG. 1, the containment vessel 46 ispreferably hermetically sealed around the melting vessel 12 to form anenclosed chamber 58. Such an enclosed chamber is preferable to having anopen space between the two vessels since any gas that exits the failedmelting vessel 12 will then also be contained within the containmentvessel 46 which would not be the case if the vessels are nothermetically sealed.

With additional reference to FIG. 2, one embodiment of the sensor 48a isillustrated as having a conduit 60 communicated with the hermeticallysealed chamber 58 between the melting vessel 12 and the containmentvessel 46 to detect a change in pressure within the hermetically sealedchamber when the melting vessel fails to thereby detect such failure.More specifically, the sensor 48a has a pressure gauge 62 which candetect the pressure change when there is a failure such as illustratedat 64 between the floor and side wall plates 50 of the melting vessel12. Such pressure change may be an increase in pressure if a vacuum isinitially drawn in the chamber 58 or may also be a decrease in pressureif the chamber is initially pressurized.

With reference to FIGS. 3 and 4, two further embodiments 48b and 48c ofthe sensor are constructed to detect failure of the melting vessel 12 bysensing the presence of material 18 received by the containment vessel46 from the failed melting vessel 12. Each of the sensors 48b and 48cincludes an electric circuit 66 that detects the presence of materialreceived by the containment vessel 46 from the failed melting vessel 12.

In the embodiment of the sensor 48b shown in FIG. 3, the electricalcircuit 66 includes a pair of electrical probes 68 that are locatedbetween the melting and containment vessels 12 and 46 and are normallyelectrically isolated from each other with their lower ends suspendedjust above the containment vessel floor plate 51 in a spacedrelationship thereto and with respect to each other. Material 18received from the melting vessel 12 upon failure thereof such as throughthe failure 64 indicated electrically connects the lower ends of theprobe 68 to complete the electrical circuit 66 and thereby provide anindication of the failure.

With reference to FIG. 4, the embodiment of the sensor 48c has theelectrical circuit 66 thereof located between the melting andcontainment vessels 12 and 46 and having a meltable fuse 70 extendingbetween the lower ends of the probes 68. When the material 18 isreceived from the failed melting vessel 12 such as through the failure64 shown, the fuse 70 is melted to open the circuit 66 as the probes 68then become electrically isolated from each other as compared to beingelectrically connected when the fuse is in place for the relative levelof electric potential between the electrical probes.

In the preferred construction of the apparatus 10 shown in FIG. 1, thereare at least two of the sensors for sensing the failure of the meltingvessel 12. These sensors are most preferably of the type illustrated inFIGS. 2, 3 and 4. More specifically, as illustrated, there are two ofthe sensors 48 having the electrical circuit 66 and are located atopposite sides of the unitized melting and containment vessels 12 and46. Suitable openings may be provided in the floor supports 54 so thatthe material received can flow back and forth so that failure at anypart of the melting vessel 12 will activate these material presencesensing type sensors. Furthermore, the apparatus 10 is illustrated ashaving the pressure sensor 48 at its upper left side as well as theother two sensors. Suitable openings can also be provided in the unshownsupports between the side wall plates 50 and 51 as well as in the floorsupports 54 so that the entire extent of the hermetically sealed chamber58 is communicated with the pressure sensor 48a for its operation whenthis type of sensor is used.

The hazardous waste vitrifying method of the invention is performed byintroducing the hazardous waste and any other necessary components forforming a glassy material upon heating through the inlet 14 into themetallic melting vessel 12. A voltage is applied across the spacedelectrical connections 72 to heat material 18 within the melting vessel12 which is located within the metallic containment vessel 46 to containany material that exits the melting vessel upon failure of the meltingvessel. Sensing of this failure by at least one of the sensors 48provides an indication that the processing should be terminated.

In performing the method for vitrifying hazardous waste, the material 18can be stirred during the heating.

As discussed above, the sensing for the failure of the melting vessel 12can be performed by detecting a change in the pressure of thehermetically sealed chamber 58 between the melting and containmentvessels 12 and 46 and can also be performed by detecting the presence ofmaterial received within the containment vessel from the failed meltingvessel, with this latter type of detection preferably being performed byan electrical circuit. Furthermore, as previously mentioned, the methodis most preferably performed by utilizing a pair of the sensors todetect failure of the melting vessel 12 in a fail-safe manner.

While the best modes for practicing the invention have been described indetail, those familiar with the art to which this invention relates willrecognize various alternative designs and embodiments for practicing theinvention as defined by the following claims.

What is claimed is:
 1. Apparatus for vitrifying hazardous waste,comprising:a metallic melting vessel for receiving hazardous waste andany other necessary components for forming a glassy material uponheating; a heater including spaced electrical connections for supplyinga voltage across the metallic melting vessel to heat the melting vesseland material within the melting vessel; a metallic containment vessel inwhich the melting vessel is located so the containment vessel uponfailure of the melting vessel receives and contains any material thatexits the melting vessel due to its failure; and a sensor that islocated externally of the melting vessel and at least partiallyexternally of the containment vessel and detects failure of the meltingvessel.
 2. Apparatus as in claim 1 wherein the melting vessel is made ofan alloy selected from the group consisting of: (a) platinum andrhodium, and (b) nickel and chromium.
 3. Apparatus for vitrifyinghazardous waste as in claim 1 further including a stirrer for mixing thematerial being heated.
 4. Apparatus for vitrifying hazardous waste as inclaim 1 wherein the sensor for detecting failure of the melting vesselsenses the presence of material received by the containment vessel fromthe failed melting vessel.
 5. Apparatus for vitrifying hazardous wasteas in claim 4 wherein the sensor includes an electrical circuit thatdetects the presence of material received by the containment vessel fromthe failed melting vessel.
 6. Apparatus for vitrifying hazardous wasteas in claim 5 wherein the electrical circuit of the sensor includes apair of electrical probes that are located between the melting andcontainment vessels and are normally electrically isolated from eachother until material received by the containment vessel from the failedmelting vessel electrically connects the probes to each other. 7.Apparatus for vitrifying hazardous waste as in claim 5 wherein theelectrical circuit of the sensor includes a flow path that is locatedbetween the melting and containment vessels and that is normally closedbut is opened by the presence of material received by the containmentvessel from the failed melting vessel.
 8. Apparatus as in claim 1further including another sensor for sensing failure of the meltingvessel.
 9. Apparatus for vitrifying hazardous waste material as in claim8 wherein one of the sensors for detecting a failure of the meltingvessel is a sensor that is communicated with a hermetically sealedchamber between the melting vessel and the containment vessel to sense achange in pressure when the melting vessel fails, and the other sensorbeing a sensor including an electrical circuit that senses the presenceof material received within the containment vessel from the failedmelting vessel.